1. Field of the Invention
The present invention relates to a thermally suppressing circuit, and more particularly to a thermally suppressing circuit for restarting a locked motor, which comprises an auto-restart function of a restart-charging drive IC, adapted to reduce an auto restart time interval for a coil by means of detecting an auto restart signal to thereby avoid destroying the motor during low motor speed, locking fan wheel, or passing overcurrent.
2. Description of the Related Art
In long-term use, a conventional fan has two abnormal situations. The first situation is accumulating a huge mass of dust which results in a decrease in motor speed. The second situation is inserting an external thing into the fan blades or the internal space of the motor which results in locking the motor. Under these two abnormal situations, the current passing the motor coil becomes tremendous and increases rapidly. The great power consumption, caused by the large current on the motor coil, may be changed to heat that results in a great increase in the temperature. Also, the increasing temperature at the motor coil may further aggravate the power consumption so that the temperature at the motor coil is increased repeatedly. Subsequently, the high temperature may deteriorate sharply the quality of the insulator of the enamel-insulated wire, which may be cracked. Consequently, the cracked insulator of the motor coil results in a short circuit that the motor may be destroyed.
During the abnormal situation the conventional motor is designed to prevent an overcurrent from passing through the motor coil, generally an auto restart function is built in a drive IC. In this manner the restart-charging drive IC restarts the motor repeatedly at each time interval during the abnormal situation. If the motor is broken down or fails to restart, the power is initially cut off and the motor is then restarted at each time interval.
FIG. 1 illustrates a circuitry of a conventional double phase brushless dc motor circuit. Referring to FIG. 1, a motor drive circuit 1 comprises a restart-charging drive IC 10, two coils 11, two transistors 12, and a restart-charging capacitor 13. The restart-charging drive IC 10 is adapted to turn on or off the transistors 12 to thereby control the coils 11. The auto restart function of the motor drive circuit 1 predetermines time intervals of ON and OFF whose ratio is adapted to control that of the charging time to the discharging time of the restart-charging capacitor 13. In responding to the ON and OFF time intervals, the motor drive circuit 1 may turn on or off the transistors 12.
FIG. 2 illustrates a circuitry of a conventional single-phase brushless dc motor circuit. Referring to FIG. 2, a motor drive circuit 2 comprises a restart-charging drive IC 20, a coil 21, and a restart-charging capacitor 22. In responding to the ON and OFF time intervals, the motor drive circuit 2 is adapted to electrically open or close the coil 21.
FIG. 3 illustrates a circuitry of a conventional double phase brushless dc motor circuit. Referring to FIG. 3, a motor drive circuit 3 comprises a restart-charging drive IC 30, two coils 31, and a restart-charging capacitor 32. In responding to the ON and OFF time intervals, the motor drive circuit 3 is adapted to electrically open or close the coils 31.
FIGS. 4A and 4B illustrate waveform diagrams of a restart-charging drive member and a restart-charging capacitor of a brushless dc motor. Referring to FIG. 4A, during a locked situation, the restart-charging drive IC outputs a high voltage signal (Hi) within a time interval T1 as the restart-charging capacitor C is charged. Alternatively, it outputs a low voltage signal (Lo) within a time interval T2 as the restart-charging capacitor C is discharged in turn. Referring to FIG. 4B, during a locked situation, the restart-charging drive IC outputs a low voltage signal (Lo) within a time interval T1 as the restart-charging capacitor C is charged. Alternatively, it outputs a high voltage signal (Hi) within a time interval T2 as the restart-charging capacitor C is discharged in turn.
Referring again to FIGS. 4A and 4B, the ratio of T1 to T2 is fixed and constant due to the unchangeable ratio of a charging time to a discharging time of the restart-charging capacitor C.
Referring again to FIGS. 1 through 4A and 4B, the motor is automatically restarted by a current with maximum power consumption within a time interval T1 when the restart-charging capacitors 13, 22, 32 are charged. The motor is repeatedly restarted at each time interval T1 as long as the locked situation is continued. As to the low speed or low power motor, the maximum power consumption of the motor may not result in greater power consumption and a vast amount of heat. As to the high speed or high power motor, a rapid overcurrent, exceeding several amperes, may pass the coil resulting in greater power consumption and a vast amount of heat when the motor is in abnormal operation. Consequently, the motor may be destroyed due to the vast amount of heat.
The present invention intends to provide a thermally suppressing circuit adapted to reduce a charging time interval of a restart-charging capacitor by means of detecting an auto-restart signal for avoiding destruction of the motor in such a way to mitigate and overcome the above problem.